The present invention relates to a rolling bearing for supporting a rotating shaft of a high speed rotating machine such as a gas turbine, or a jet engine.
Conventionally, in order to support a rotating shaft, rolling bearings such as a ball bearing shown in FIG. 8, and a roller bearing shown in FIG. 11 are widely used. The ball bearing shown in FIG. 8 provides an outer race 2 having an outer raceway 1 on the inner face, an inner race 4 having an inner raceway 3 on the outer face, and a plurality of balls 5 (rolling elements) which are rotatably disposed between the outer and inner raceways 1 and 3. The balls 5 are held by a cage 6 with being arranged at regular spaces in the circumferential direction.
In the ball bearing shown in FIG. 8, the inner race 4 is of the two-piece type. Specifically, the inner race 4 has a configuration in which paired left and right half pieces 7a and 7b having an annular shape are laterally joined to each other. The inner raceway 3 are formed at the joint portion of the two half pieces 7a and 7b. Since the balls 5 contacts with the inner raceway 3 at an angle of contact which is indicated by a chain line i, however, the rolling contact surface of the balls 5 do not contact with the joint face of the two half pieces 7a and 7b.
In the half piece 7a which is the one (the left one in FIG. 8) of the half pieces 7a and 7b, a groove 8, and an oil hole 9 are formed as shown in FIGS. 9 and 10. The groove 8 is formed in an inner end edge of the half piece 7a. When the half piece 7a is combined with the other half piece 7b, the groove 8 constitutes an oil path which opens on the center portion of the inner raceway 3. The oil hole 9 opens on a portion which is in an outer face of an end portion of the half piece 7a in the axial direction (the lateral direction in FIG. 8), and which is separated from the inner raceway 3. Moreover, also the other half piece 7b is provided with an oil hole 10 which opens on a portion which is in an outer face of an end portion of the other half piece 7b in the axial direction, and which is separated from the inner raceway 3.
When a high speed rotating machine into which such a rolling bearing is incorporated is operated, lubricating oil is supplied from a rotating shaft supported on the inner side of the inner race 4, into the groove 8 and the oil holes 9 and 10. As a result, contact portions between the balls 5 and the outer and inner raceways 1 and 3, and sliding contact portions between the outer face of the inner race 4 and the inner face of the cage 6 are lubricated.
The roller bearing shown in FIG. 11 provides an outer race 2a having an outer raceway 1a on the inner face, an inner race 4a having an inner raceway 3a on the outer face, and a plurality of rollers 11 (rolling elements) which are rotatably disposed between the outer and inner raceways 1a and 3a. The rollers 11 are held by a cage 6a with being arranged at regular spaces in the circumferential direction.
In the roller bearing, oil holes 9a and 10a are formed at the both end portions of the inner race 4a in the axial direction, respectively, so that lubricating oil can be supplied to contact portions between the rollers 11 and the outer and inner raceways 1a and 3a, and sliding contact portions between the outer face of the inner race 4a and the inner face of the cage 6a.
However, rolling bearings such as a ball bearing, and a roller baring having the configurations described above have the following problem to be solved. When the inner race 4 or 4a is rotated at a high speed together with a rotating shaft of a high speed rotating machine into which such a rolling bearing is incorporated, a tensile force in the circumferential direction and due to a centrifugal force is applied to the inner race 4 or 4a.
This tensile force causes stresses to concentrate on the oil holes 9 and 9a or 10 and 10a formed in the inner race 4 or 4a. In such a conventional rolling bearing, all the oil holes 9 and 9a or 10 and 10a have a circular section shape, and therefore the degree of stress concentration is very high. When the inner race 4 or 4a is rotated at a high speed for a long period, there arises a possibility that a defect such as a crack is produced. Conventionally, therefore, the rotation speed of the inner race 4 or 4a is limited to a level at which such a defect is not produced. With respect to the groove 8 formed in the ball bearing shown in FIGS. 8 to 10, such stress concentration is hardly produced. However, the oil supply path formed by the groove 8 cannot be located at a portion other than the joint face of the half pieces 7a and 7b, resulting in that the oil supply path formed by the groove 8 fails to substitute for the oil holes 9 and 9a or 10 and 10a
In the above, stress concentration due to the section shape of the oil holes 9 and 9a or 10 and 10a through which lubricating oil passes has been described. Such stress concentration is produced also at holes other than the oil holes. In some cases, in order to measure the temperature of the inner race 4 during an operation process, recess holes 14 are formed in the inner race 4 as shown in FIG. 12, and temperature sensors are disposed in the recess holes 14, respectively. In a conventional rolling bearing, such recess holes 14 also have a circular section shape in the same manner as oil holes, and therefore such stress concentration is produced.